Conventionally, in the semiconductor device manufacturing field, for example, so-called dry etching for etching a desired portion by an effect of a plasma produced from a certain etching gas has been widely used to form a fine circuit structure of a semiconductor device.
Further, recently, also in other devices having a fine structure besides a semiconductor device, their fine structures are manufactured by performing dry etching for etching desired portions according to a pattern shape of a mask, instead of a mechanical cutting and the like.
With regard to such dry etching, when silicon oxide is plasma-etched, for example, a gaseous mixture of gas containing carbon and fluorine, oxygen gas and inert gas is used. More specifically, for example, a gaseous mixture which contains C5F8 gas, O2 gas and Ar gas is used.
However, as a result of extensive researches conducted by the present inventors, the following issue was identified in the aforementioned etching process. Namely, as shown in FIG. 6A, when a mask material layer 102 with a desired pattern is formed on a silicon oxide film (e.g., thermal oxide film) 101 which is on a semiconductor wafer W, thereafter, as shown in FIG. 6B exposed parts of the silicon oxide film 101 are plasma-etched according to the pattern shape of the mask material layer 102 by using a gaseous mixture of C5F8 gas, O2 gas and Ar gas to form grooves (trenches) 103 on the silicon oxide film 101, as shown by the dotted lines, the issue is that undesirable grooves, i.e., so-called microtrenches, are formed on the base portions of sidewalls (the angled portions of the grooves 103's bottom portions) where approximately right-angled portions should be formed.
Here, in order to numerically estimate the production of such microtrenches, the etching depth of the silicon oxide film 101 of its flat portion indicated by arrow A excluding the microtrench portion and the etching depth of the silicon oxide film 101 of the microtrench portion indicated by arrow B in FIG. 6B are measured, and then their ratio (B/A) (hereinafter, referred to as a microtrench coefficient) is obtained. Further, in an assessment using a microtrench coefficient, it is preferable that the microtrench coefficient is approximately 1, but in a case such as the example shown in FIG. 6B, as will be discussed later, the value of the above-mentioned microtrench coefficient is greater than or equal to 1.14.
If microtrenches as above are formed, for example when wiring materials or other materials are buried in the grooves (trenches), it is possible to have a problem such that the materials are not sufficiently buried in the microtrench portions thereby forming a gap. Further, when being used as a machine component and the like, it is possible to have a problem such that the component's mechanical strength is undermined because of the existence of microtrenches. Therefore, the formation of microtrenches as above should be prevented as much as possible.